It comes 15 years after work began on the project, which is still waiting for approval from US authorities.

“Resolution is one of the most significant undeveloped copper deposits in the world and this additional funding demonstrates Rio Tintos commitment to bring the mine into production,” said chief executive Jean-Sebastien Jacques.

The project is in its seventh year of an environmental review and approval process by the US Forest Service. The environmental impact study is expected to be completed next year.